In recent years, there have been proposed a technology whereby the image of text or picture or the like printed on a sheet or other recording media is formed on a coloring material that can erase the image. As the cycle of formation of image on the sheet made of an erasable coloring material and then erasure of the image is carried out repeatedly, a single sheet can be reused repeatedly in multiple rounds, so that it contributes to conservation of resources.
In order to enable erasure by the erasable coloring material, for example, blue color or other prescribed color may be used.
When an image sensor of an image reading apparatus is used to read an image, a light source emits light to illuminate the surface of the original, and the image is read. For the image forming apparatus, for the purpose of ecology, there is a type of image printed using a special toner that allows fixing at a lower temperature and erasure of the printed text or picture at a higher temperature. In order to recycle the paper sheet, the aforementioned toner uses a special color, such as blue color to ensure that the print is not remarkable in erasure.
Because the light source adopted in reading the blue image is a conventional light source (white light source) for read and it contains a blue color component, the read image become lighter. As this image data are converted to a monochromic image, the obtained image becomes even lighter.